MP3 Player Soft Power On Circuit w/ Play

PC1 .68UF - Input noise filter cap.
PC2 1UF - LM2825 input noise filter cap.
PC3 150UF - Low ESR LM2825 output filter cap
PC4 .1UF - Soft Start up Cap as required by datasheet
PD1 1N5404 - Polarity Protection diode
PD2 - PD3 - MBR745 - High current schottky diodes used for blocking
PD2 - blocks external power from battery pack
PD3 - blocks output of LM317 from relative positive voltage compared to input
PD4 - PD6 - 1N4004 - used to drop 5v to 3.x volts for 3v parts
PD7 - PD8 - 1N4004 - used in single button power on circuit/play button circuit
PD7 - protects MCU output line from high voltage
PD8 - keep 'PLAY' line from sensing PWRCNT line coming from MCU
PIC1 - LM2825 - single chip step down switching regulator
PIC2 - LM317 - voltage regulator used in constant current mode to recharge battery pack at approx 100ma
PJ1 - 12v external input jack
PJ2 - jack to internal 8 cell NiCad/NiMH battery pack
PR1 - 33K / PR2 - 10K - voltage divider for use with MCU's A/D converter to sense battery pack/input voltage
PR3 - 120ohm - set resistor for constant current regulator
PR4 - 1K - used to provide a bit of a load for diode voltage dropping string
PR5 - 4.7Kohm / PR7 - 4.7Kohm - used as voltage divider for Switch so tap off to 'Play' line won't be too high
PR6 - 4.7Kohm - used as a pull down for PWRCNT line (if SS/SD line is floating, LM2825 will remain on)
PS1 - SWITCH - combination power on/Play mode switch (NO push button switch)

As stated previously, if the LM2825's SS/SD line remains floating, the system will stay on, so it's pulled to ground using PR6.
When the system is off, the PWRCNT line is floating, being pulled down, the LM2825 remains off.
When the Power/Play switch is pressed, the voltage is divided thru PR5/PR7, goes thru PD8 and ends up at the SS/SD line on the LM2825. Thru the use of PC4, the LM2825 will 'soft' turn on. The regulator will turn on, supplying 5v to the system, which then the PIC will start up. After a bit of housekeeping by the PIC, it will turn on PWRCNT which will in turn provide a 5v (a bit less) signal to the SS/SD line holding the regulator in the on state. The Power/Play button can then be released.
While the system is on, the Power/Play button can also be used as a PLAY button. With the switch not being pressed, the 'PLAY' line is being pulled to ground thru PR7 and isolated from PWRCNT thru PD8. When the button is pressed, battery voltage is applied to the PR5/PR7 voltage divider with the middle going out to the '574 latch, where it should be read as a high indicating a closed switch. This shouldn't interfere with PWRCNT line and associated parts.